EP3384594B1 - Method and device for evaluating the energy produced by an electric arc in photovoltaic apparatus - Google Patents

Description

Technical field of the invention

The invention relates to a method and a device for evaluating the energy produced by an electric arc in a photovoltaic installation. It also relates to a photovoltaic installation equipped with such a device.

State of the art

Photovoltaic installations are likely to be the seat of electric arcs. The documents F. Schimpf and L. Norman, 31st International Telecommunication Energy Conference, Incheon, Korea, 18-22 Oct 2009, IEEE, Piscataway, NJ, USA, 1-6, XP031579534 ; and K. Kozyi et al., IEEE Transactions on Power Delivery, IEEE Service Center, New York, US, vol. 28, n.3, 1584-1591, XP011515987 describe methods for evaluating the energy produced by an electric arc.

An electric arc can occur in the event of a conductor fault or a faulty connection (eg due to the opening of a charging connector or corrosion of a conductor). It is made by a plasma that appears between two electrodes. These can be constituted by the two ends of a conductor or by two parts of an open or locally interrupted connector (due to corrosion for example). The appearance of an electric arc is accompanied by a front or short voltage positive jump, of the order of a few microseconds. The initial arc voltage V _arc0 has a value which is characteristic of the appearance of an electric arc and which depends on the material of the electrodes. It is generally between 10V and 30V. For example, in the case of copper electrodes, the initial arc voltage V _arc0 is of the order of 20V. The plasma of the electric arc plays the role of a resistance that increases over time. The initial voltage front is therefore generally followed by a gradual increase of the arc voltage up to reaching an open circuit voltage.

Photovoltaic installations have the characteristic of operating at continuous electrical current and voltage, which can be problematic in case of appearance of an electric arc related to a defect. Indeed, in current and DC voltage, there is no natural extinction of the electric arc by zero crossing of the voltage and current, as is the case in alternating current. As a result, an electric arc linked to a defect is likely to generate a plasma generating a very high heat for a long time and thus producing a lot of energy within a photovoltaic installation. Such a plasma is destructive and can cause a start of fire. For safety reasons, it is therefore essential to detect the presence of a potential arc in a photovoltaic installation and to interrupt it in good time to avoid any deterioration or start of fire. For this purpose, the photovoltaic system is equipped with an arc detection device, or arc detector. This is usually associated with an intervention or arc extinguishing device, intended to intervene to interrupt the electric arc and prevent any deterioration or start of fire.

An electric arc can also occur, in normal operation, in an electromagnetic control and / or protection member, the opening or closing of contacts or poles. For example, an isolating switch generates, at the opening, an electric arc of a duration less than or equal to a known maximum duration. Arc extinguishing means generally allow the arc to be interrupted so that it does not persist beyond a predefined maximum arc duration.

There are various methods, some very fast, to detect the presence of an arc in a photovoltaic system. In the event of an electric arc connected to the opening in charge of a disconnecting switch or other electromechanical device, this may cause a positive detection of arc followed by an inadvertent shutdown of the photovoltaic installation, which is not not desirable.

Moreover, an electric arc related to a defect in the photovoltaic installation can have a duration ranging from a few microseconds to several minutes or even hours in certain special conditions. For example, in the case of a discontinuous electric arc composed of a succession of micro-arcs of short duration, separated by periods without arc, each micro-arc is a priori not dangerous in itself but the Energy accumulated by the succession of these micro-arcs can become critical for the environment and / or installation over time.

For the reasons that have just been mentioned, it appears useful to evaluate the energy level released by an electric arc, in particular to assess its dangerousness for the photovoltaic installation and / or the environment.

Object of the invention

1. A) Mesure d'un signal de courant électrique produit par l'installation avec une fréquence d'échantillonnage supérieure ou égale à 50 kHz, et, à partir du signal de courant mesuré :
   • ∘ Détermination d'une valeur initiale du courant avant apparition d'un arc électrique ;
   • ∘ Détermination de valeurs de courant pendant l'arc électrique ;
2. B) Evaluation de valeurs d'une tension d'arc à partir des valeurs de courant déterminées pendant l'arc et de la valeur initiale du courant;
3. C) Intégration dans le temps du produit des valeurs de tension d'arc évaluées par les valeurs de courant déterminées, afin de déterminer l'énergie de l'arc.

To this end, the invention relates to a method for evaluating the electrical energy produced by an electric arc in a photovoltaic installation comprising the following steps:

1. A) Measurement of an electrical current signal produced by the installation with a sampling frequency greater than or equal to 50 kHz, and from the measured current signal:
   • ∘ Determination of an initial value of the current before the appearance of an electric arc;
   • ∘ Determination of current values during the electric arc;
2. B) Evaluation of values of an arc voltage from the current values determined during the arc and the initial value of the current;
3. C) Integration over time of the product of the arc voltage values evaluated by the determined current values, in order to determine the energy of the arc.

According to the invention, the electrical energy generated by an electric arc occurring within the photovoltaic installation is evaluated from a simple measurement of the current produced by the installation, at a frequency high sampling rate. The measuring device may therefore comprise a simple current measurement sensor.

In a particular embodiment, to evaluate each arc voltage value, the difference between a current value during the determined arc and the initial current value is calculated and said difference is multiplied by the ratio between a jump amplitude. voltage related to the appearance of the electric arc and a current jump amplitude related to the appearance of the electric arc.

According to the invention, the arc voltage is evaluated from the measured current. This evaluation is based on a linear reconstruction from the measured current. Each arc voltage value evaluated is proportional to the difference between a current value during the arc and the initial current, by a proportionality factor which is equal to the ratio between the amplitude of the voltage jump and the amplitude. of the current jump, related to the appearance of the arc.

Advantageously, the method comprises a step of decomposing the current signal into a plurality of acquisition windows, and, for each acquisition window, a step of determining an average value of the current, said average value being stored in memory. .

In a particular embodiment, during the integration step, an arc energy is calculated for each acquisition window by making the product of the average value of the current measured on said window, the value of evaluated voltage and a duration of the acquisition window, and then the sum of the calculated arc energies relating to a succession of acquisition windows

In an alternative embodiment, in the case of a discontinuous electric arc comprising a plurality of micro-arcs, steps B) and C) are used to determine the energy of each electric micro-arc, and then the sum of the respective energies of the electric micro-arcs to determine the energy of the discontinuous electric arc.

In a particular embodiment, the initial value of the current is equal to the average value of the current relative to at least one acquisition window preceding that which contains the current jump.

The value of the voltage jump can be predefined and between 12V and 35V, for example equal to 20V.

Advantageously, the amplitude of the current jump is determined from the measured current signal.

In a particular embodiment, the method comprises a step of comparing the energy of the determined electric arc with an energy threshold and a safety step in case of exceeding said threshold.

• un module d'obtention d'un signal de courant électrique produit par l'installation ;
• un module de traitement du signal de courant, adapté pour déterminer une valeur initiale du courant avant apparition d'un arc électrique et des valeurs de courant pendant l'arc électrique ;
• un module d'évaluation de valeurs de tension d'arc à partir des valeurs de courant déterminées et de la valeur initiale du courant ;
• un module d'intégration dans le temps du produit des valeurs de tension d'arc évaluées par les valeurs de courant déterminées, afin de déterminer l'énergie de l'arc.

The invention also relates to a device for evaluating the energy released by an electric arc in a photovoltaic installation, characterized in that it comprises:

• a module for obtaining an electrical current signal produced by the installation;
• a current signal processing module, adapted to determine an initial value of the current before arcing and current values during the electric arc;
• a module for evaluating arc voltage values from the determined current values and the initial value of the current;
• a time integration module of the product of the arc voltage values evaluated by the determined current values, in order to determine the energy of the arc.

• le module d'évaluation de valeurs de tension d'arc est adapté pour calculer la différence entre une valeur de courant pendant l'arc déterminée et la valeur initiale de courant et multiplier ladite différence par le rapport entre une amplitude de saut de tension lié à l'apparition de l'arc électrique et une amplitude de saut de courant lié à l'apparition de l'arc électrique ;
• le module de traitement du signal de courant est adapté pour décomposer le signal de courant en une pluralité de fenêtres d'acquisition, et, pour chaque fenêtre d'acquisition, déterminer une valeur moyenne de courant mesuré sur ladite fenêtre, ladite valeur moyenne de courant étant enregistrée en mémoire ;
• le module d'intégration est agencé pour calculer, pour chaque fenêtre d'acquisition, une énergie d'arc en faisant le produit de la valeur moyenne du courant mesuré sur ladite fenêtre, de la valeur de tension évaluée et d'une durée de la fenêtre d'acquisition, puis pour faire la somme des énergies d'arc calculées relatives à une succession de fenêtres d'acquisition.

The device advantageously comprises all or part of the following additional features:

• the arc voltage value evaluation module is adapted to calculate the difference between a current value during the determined arc and the initial current value and to multiply said difference by the ratio between a voltage jump amplitude related to the appearance of the electric arc and a current jump amplitude related to the appearance of the electric arc;
• the current signal processing module is adapted to decompose the current signal into a plurality of acquisition windows, and, for each acquisition window, to determine an average current value measured on said window, said average current value being stored in memory;
• the integration module is arranged to calculate, for each acquisition window, an arc energy by making the product of the average value of the current measured on said window, the evaluated voltage value and a duration of the acquisition window, then to sum the calculated arc energies relative to a succession of acquisition windows.

The invention also relates to a security system for a photovoltaic installation, characterized in that it comprises a device for detecting an electric arc, a device for evaluating the energy released by the detected electric arc, such as defined above, and an intervention device for putting the photovoltaic system safe in the event of an electric arc.

The invention also relates to a photovoltaic installation comprising the security system defined above.

Brief description of the drawings

• La figure 1 représente un schéma d'une installation photovoltaïque selon un exemple de réalisation de l'invention ;
• La figure 2 représente un exemple de signal mesuré de courant électrique produit par l'installation de la figure 1, intégrant un saut de courant lié à un arc électrique ;
• La figure 3 représente un premier exemple d'un signal de courant électrique produit par l'installation photovoltaïque de la figure 1, décomposé en fenêtres d'acquisition et intégrant un saut de courant lié à l'apparition d'un arc électrique continu au sein de l'installation ;
• La figure 4 représente un deuxième exemple d'un signal de courant électrique produit par l'installation photovoltaïque de la figure 1, décomposé en fenêtres d'acquisition et intégrant plusieurs sauts de courant liés à des micro-arcs électriques au sein de l'installation ;
• La figure 5 représente un exemple de la caractéristique courant-tension d'un module photovoltaïque de l'installation de la figure 1 et la courbe correspondante de puissance en fonction de la tension ;
• La figure 6 représente un organigramme des étapes du procédé d'évaluation, selon un mode de réalisation particulier de l'invention ;
• La figure 7 représente un schéma bloc fonctionnel du dispositif d'évaluation selon une forme de réalisation particulière de l'invention, adapté pour mettre en oeuvre le procédé de la figure 5.

The invention will be better understood with the aid of the following description of a particular embodiment of the method and of the device for evaluating the energy produced or generated by an electric arc in a photovoltaic installation, a system of security for a photovoltaic installation integrating such an evaluation device and a photovoltaic installation equipped with this security system, with reference to the appended drawings in which:

• The figure 1 represents a diagram of a photovoltaic installation according to an exemplary embodiment of the invention;
• The figure 2 represents an example of a measured signal of electric current produced by the installation of the figure 1 , incorporating a current jump linked to an electric arc;
• The figure 3 represents a first example of an electrical current signal produced by the photovoltaic plant of the figure 1 , broken down into acquisition windows and integrating a jump of current related to the appearance of a continuous electric arc within the installation;
• The figure 4 represents a second example of an electrical current signal produced by the photovoltaic plant of the figure 1 , decomposed into acquisition windows and incorporating several current jumps related to micro-arcs within the installation;
• The figure 5 represents an example of the current-voltage characteristic of a photovoltaic module of the installation of the figure 1 and the corresponding power curve as a function of the voltage;
• The figure 6 represents a flowchart of the steps of the evaluation method, according to a particular embodiment of the invention;
• The figure 7 represents a block diagram functional evaluation device according to a particular embodiment of the invention, adapted to implement the method of the figure 5 .

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS OF THE INVENTION

The invention aims to evaluate the energy generated or produced by an electric arc occurring within a photovoltaic installation 100.

On the figure 1 schematically shows an example of a photovoltaic installation 100 capable of producing a direct current I. This comprises, in known manner, several photovoltaic modules (PV) 1 connected to an inverter 2. The PV modules 1 are here identical. PV1 modules can be connected in series, parallel or combined. A string of series-connected PV modules is called a string. For example, as shown on the figure 1 , the installation 100 comprises several strings, or chains, of m PV modules 1, connected in parallel. The inverter 2 is intended to convert the direct current I produced by the photovoltaic modules 1 into an alternating current and to supply it to an electrical network 3.

The method of the invention seeks to evaluate the energy released or produced by an electric arc whose presence is detected in a photovoltaic installation 100. An electric arc can be linked to a defect and occur anywhere in the field. 100, for example between the photovoltaic modules 1 and the inverter 2 (as represented by the electric arc 4 on the figure 1 ), or within a photovoltaic module 1, or on a link connecting in series several photovoltaic modules 1 (as represented by the electric arc 4 'on the figure 1 ). An electric arc can also occur during normal operation of the installation 100, in an electromechanical device, for example in a disconnector switch (not shown in FIG. figure 1 ), at the opening in charge of the contacts of this one. In this case, the member is provided with arc extinguishing means for quickly extinguishing the electric arc.

An electric arc, whether linked to a fault or not, causes a significant variation in voltage within the electrical installation 100. Indeed, the appearance the electric arc is characterized by a front or positive voltage jump, of a duration of the order of a few microseconds and an amplitude equal to an initial arc voltage V _arc0 characteristic. The value of this initial arc voltage V _arc0 is typically between 12V and 35V. It depends on the material constituting the electrodes between which the electric arc is formed. For example, if the electrodes are copper, the initial arc voltage V _arc0 is equal to, or substantially equal to, 20V. When an electric arc appears in the photovoltaic installation 100, whether it is an electric arc linked to a defect (for example the arc 4 or 4 ') or an electric arc connected to the opening in charge of the disconnecting switch, the voltage across one or more photovoltaic modules 1 (in the event that the arc occurs outside the module or modules considered) increases sharply due to the voltage of initial arc V _arc0 and the current I produced by the photovoltaic system also decreases abruptly by a value Δl _arc0 . This value Δl _arc0 depends on the position of the operating point on the current-voltage curve, or characteristic curve IV, of the photovoltaic module or modules. On the figure 5 a voltage jump of 20V is shown from the maximum power point MPP of one or more PV modules and the corresponding current jump ΔI _arc0 , caused by the occurrence of an electric arc. On the figure 2 As an illustrative example, there is shown a negative current jump related to the appearance of an electric arc, in this case a continuous arc of long duration caused by a defect within the photovoltaic system 100.

• F_i, avec 1 ≤ i ≤ N, avant apparition de l'arc, et
• F_arcj, avec 1 ≤ j, à compter de l'apparition de l'arc.

On the figure 3 a first example of an electric current signal I produced by the photovoltaic system 100 and measured by a current measurement sensor is shown. This signal integrates a negative current jump linked to the appearance of a long-lasting continuous electric arc caused by a fault. The current signal is decomposed into a succession of acquisition windows, each acquisition window having a duration between 10 μs and 100 ms, noted:

• F _i , with 1 ≤ i ≤ N, before appearance of the arc, and
• F _arcj , with 1 ≤ j , from the appearance of the arc.

On the figure 4 a second example of an electric current signal I produced by the photovoltaic installation 100 and measured by a current measuring sensor is shown. The signal integrates a negative current jump linked to the appearance of a discontinuous electric arc comprising a succession of micro-arcs (that is to say short electric arcs, typically between 2 μs and 100 μs ) separated by periods without arc. The current signal is decomposed into a succession of acquisition windows. On the figure 4 , only the acquisition window containing the beginning of the electric arc is shown. An electric arc of this type is generally related to a connection fault (contact oxidation, solder rupture, terminal block loosening, etc.). In the presence of such a connection fault, electrodes are formed but remain by construction very close to each other, or even in random contact, which induces random electrical connections. An electric arc can appear between these electrodes, lasting a few microseconds to a few hundred microseconds. By melting the electrode materials, a solder bridge can be created, thereby restoring the electrical contact between the electrodes, and then breaking again under the joule effect of the current thus causing the appearance of a new arc of short duration . This alternation of occurrence and disappearance of arc of short duration can be repeated several times and thus generate a succession of electric arcs of short durations separated by periods without arc.

The photovoltaic installation 100 furthermore comprises a sensor 5 for measuring the electric current I produced by the installation 100, a device 7 for detecting an electric arc, a device 8 for evaluating the energy released by an electric arc detected. and a device 9 intervention or security.

The current measuring sensor 5 comprises, for example, a resistor 50, such as a shunt resistor, placed on an electrical connection of the photovoltaic installation 100 (for example at the input of the inverter 2 as shown in FIG. figure 1 ), and a voltage measuring sensor 51 for measuring the voltage across the resistor 50 which is the direct image of the current I by a known proportionality factor. The current I supplied by the photovoltaic system 100 is in fact proportional to the voltage U across the resistor 50, according to the relation: I = 1 / R * U (where R represents the value of the resistor 50). The voltage U measured here is therefore the image of the direct current I delivered by the photovoltaic installation 100. However, it would be possible to use a current measurement sensor of another type. The current measurement sensor 5 operates at a high sampling frequency, here greater than or equal to 50 kHz. In the example described here, the sampling frequency is equal to 200 kHz.

The measurement sensor 5 is connected to a buffer memory 6 intended in particular for storing the measured current signal.

The function of the arcing detection device 7 is to detect an electric arc occurring in the photovoltaic installation 100. It is adapted to implement an electric arc detection method, preferably capable of rapidly detecting the arcing. arcing, preferably within a few hundred microseconds after this occurrence. The detection method may be based on the detection of a positive voltage jump, as described for example in the patent document FR3002645 , or on a measurement of current, in particular on the detection of a negative current jump related to the appearance of the arc as described in the French patent application filed under the number 1561622 . The detection device 7 is connected to one or more sensors for measuring voltage or current, according to the method of arcing detection implemented by communication links. Since the installation is equipped with a high frequency current measuring sensor 5, the electric arc detection could advantageously be based on the measurement of the current.

• un module 80 d'obtention d'un signal de courant électrique produit par l'installation ;
• un module 81 de traitement du signal de courant obtenu ;
• un module 82 d'évaluation de la tension d'arc ;
• un module 83 de détermination de l'énergie de l'arc ;
• une unité de traitement ou de contrôle 84, en l'espèce un microprocesseur, à laquelle sont reliés tous les modules 80 à 83 et destinée à en contrôler le fonctionnement ;
• une mémoire 85.

The device 8 for evaluating the energy released by a detected electric arc serves to evaluate the quantity of energy produced or released by an electric arc detected by the detection device 8. It comprises the following modules:

• a module 80 for obtaining an electric current signal produced by the installation;
• a module 81 for processing the current signal obtained;
• a module 82 for evaluating the arc voltage;
• a module 83 for determining the energy of the arc;
• a processing or control unit 84, in this case a microprocessor, to which all the modules 80 to 83 are connected and intended to control its operation;
• a memory 85.

The module 80 for obtaining the current signal is connected to the buffer memory 6 which stores the current signal measured by the measurement sensor 5.

The processing module 81 is adapted to decompose the measured current signal into a plurality of acquisition windows denoted F _x . Each window contains a number N _f of acquisition points (i.e., measured / sampled voltage values). For each acquisition window F _x , the module 81 calculates an average value of the voltage measured on the window, denoted V _Fx . The average voltage values relating to the various acquisition windows F _x are stored in memory 85. Thus, the voltage values determined during an arc, denoted by V _Farcj , correspond to the calculated average voltage values relating to the acquisition windows F _arcj. during the electric arc. Moreover, the processing module 81 is intended to determine an initial value of the current before the appearance of an electric arc, the amplitude of a current jump linked to the appearance of an electric arc and current values after appearance of the electric arc, from the measured current signal, as will be described in the description of the method.

The module 82 is intended to evaluate arc voltage values from the current values determined during the arc and from the initial value of the arc. current, as will also be described in more detail in the description of the process.

The module 83 is intended to determine the energy of an electric arc by time integration of evaluated arc voltage values and current values determined during the arc, as will be described in more detail in the description of the present invention. process.

The modules 81, 82 and 83 are software modules intended to be executed by the processing unit 84 for carrying out steps of the evaluation method which will be described below. The processing unit 84 is also intended to transmit a safety command to the intervention device 9, in the event of detection of an electric arc, in particular of an electric arc having released a critical energy. The intervention device 9 has the role of interrupting such an electric arc, to avoid any risk of damage or fire. The energy evaluation device 8 is connected to the intervention device 9 by a communication link 10.

The arcing detection device 7, the device 8 for evaluating the electrical energy produced by the detected electric arc and the intervention device 9 form a security system for photovoltaic installation 100.

We will now describe a particular embodiment of the method for evaluating the electrical energy produced by an electric arc detected in the photovoltaic installation 100, with reference to FIG. figure 6 .

The method comprises a step E0 of acquisition or measurement, here by the measuring sensor 5, of an electric current signal I produced by the installation 100. The measured current signal I is here stored in memory 6 and can obtained by the module 80 of the energy evaluation device 8. The measured signal is sampled with a sampling frequency F _ech high, greater than or equal to 50 kHz, for example equal to 200 kHz.

Pour chaque fenêtre d'acquisition F_x, le module de traitement 81 calcule une valeur moyenne de la tension mesurée sur la fenêtre, notée V_Fx, en faisant la moyenne des points d'acquisition de la fenêtre, lors d'une étape E2. Ces valeurs moyennes de tension V_Fx sont stockées en mémoire 85.The measured current signal I is decomposed into a succession of acquisition windows F _x during a step E1. This is implemented by the signal processing module 81. Each acquisition window F _x contains a predefined fixed number N _f of sampled current values (or acquisition points). The acquisition windows therefore have a fixed duration, here equal to $\frac{{\mathrm{NOT}}_f}{F_{\mathit{ech}}}.$

For each acquisition window F _x , the processing module 81 calculates an average value of the voltage measured on the window, denoted V _Fx , by averaging the acquisition points of the window, during a step E2. These average values of voltage V _Fx are stored in memory 85.

The method comprises a step E3 of detection of an electric arc, implemented by the arc detection device 7. This detection step E3 aims to detect an electric arc occurring in the photovoltaic installation 100. As previously indicated , the detection may be based on any known method of arcing detection, preferably adapted to quickly detect the arc within a maximum of a few hundred microseconds after its appearance.

• F_i, avec 1≤i≤N, les fenêtres antérieures à l'apparition de l'arc,
• F_arc1, la fenêtre contenant un saut de courant lié à l'apparition de l'arc, et
• F_arcj avec 1<j, les fenêtres postérieures à l'apparition de l'arc.

We notice :

• F _i , with 1≤i≤N, the windows prior to the appearance of the arc,
• F _arc1 , the window containing a current jump linked to the appearance of the arc, and
• F _arcj with 1 <j, the windows posterior to the appearance of the arc.

Suppose that an electric arc, for example an electric arc such as that represented on the figure 3 , is detected in step E3. Note T0 _arc the instant of appearance of the electric arc. At this time T0 _arc , a negative current jump occurs in the current signal, as it appears on the figure 3 .

During a step E4, the energy evaluation device 8 determines an initial value, or nominal, I ₀ of the current I before the appearance of the electric arc. In the particular embodiment described here, it calculates the average value of the current relative to the acquisition window F _N preceding the window F _arc1 which contains the current jump linked to the appearance of the arc at time T0 _bow . The initial value I ₀ of the current before the appearance of an electric arc is therefore equal to the average value of the current during the window F _N preceding the appearance of the arc. Alternatively, one could calculate the average of the current on several acquisition windows prior to the appearance of the arc to determine the initial current I ₀ .

In a subsequent step E5, the energy evaluation device 8 determines the amplitude ΔI _arc0 of the current jump related to the appearance of the electric arc. For this purpose, it calculates for example the average value of the current I _arc1 after the current jump during the acquisition window F _arc1 and then the difference between this current value I _arc1 and the initial value of the current I ₀ . Step E4 is implemented by the module 81 for processing the current signal.

The method continues with a step E6 in which the energy evaluation device 8 determines current values I _Farcj during the electric arc, corresponding to the average values of the current measured on the acquisition windows F _arcj subsequent to the appearance of the electric arc (with j> 1). Step E6 is implemented by the processing module 81. The determined current values I _Farcj are stored in memory 85.

The method then comprises a step E7 for evaluating values of the arc voltage, denoted by V _arcj , relating to the acquisition windows F _arcj during the presence of the electric arc. In the embodiment described here, the values of the arc voltage are evaluated from the determined current values I _Farcj determined during the arc and from the initial value of the current I ₀ . To evaluate each arc voltage value V _arcj , the difference between a current value during the determined arc I _Farcj and the initial value of current I ₀ is calculated and this difference is multiplied by the ratio between a jump amplitude of voltage ΔV _arc0 and a corresponding amplitude (in absolute value) of current jump Δi _arc0 , related to the appearance of the electric arc. In other words, the arc voltage V _{arcj is estimated} by the following relation: $$V_{\mathit{arcj}}=\frac{\left(I_{\mathit{Farcj}}-I_0\right)}{\left|\mathrm{\Delta }{I}_{\mathit{bow}0}\right|}*\mathrm{\Delta }{V}_{\mathit{bow}0}$$

The value of Δ V _arc voltage jump ₀ is predefined, as previously explained. It is here between 12V and 35V. In the embodiment described here, it is set at 20V.

Step E7 is implemented by the module 82 for evaluating the arc voltage.

1. a) Calcul de l'énergie d'arc pour chaque fenêtre d'acquisition pendant l'arc électrique, puis
2. b) Calcul de la somme des énergies d'arc ainsi calculés pour une succession de fenêtres d'acquisition couvrant l'arc électrique.

Then, during a step E8, the energy evaluation device 8 calculates the energy of the detected electric arc, by integrating the product of the evaluated arc voltage values V _Farcj with the values of time. determined current I _Farcj . Integration over time can be achieved by implementing the following substeps:

1. a) Calculation of the arc energy for each acquisition window during the electric arc, then
2. b) Calculation of the sum of the arc energies thus calculated for a succession of acquisition windows covering the electric arc.

Thus, during a substep E8a), the arc energy E _Farcj is calculated for each window F _arcj (that is to say the energy generated by the arc during a window F _arcj ) according to the following relation: $$E_{\mathit{Farcj}}=V_{\mathit{Farcj}}\times I_{\mathit{Farcj}}\times \tau ,\mathrm{or}\tau =\frac{{\mathrm{NOT}}_f}{F_{\mathit{ech}}}$$

Then, during a substep E8b), we calculate the total electric arc energy generated by the arc during a number n of successive windows F _arcj , n being the total number of windows F _arcj at the instant considered, by the following relation: $$F_{\mathit{arctot}}={\displaystyle {<figure-callout\; id="1"\; label="\Sigma \; FARC"\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">\Sigma \; </figure-callout>}_{\mathit{FARC}}^{\mathit{}1}{E}_{\mathit{Farcj}}}$$

The step E8 is implemented by the module 83 for determining the arc energy throughout the duration of the arc and, if necessary, repeated at each new acquisition window in order to update the determined value. arc energy.

The step E8 for evaluating the energy E _arctot generated or produced by the electric arc can be followed by a test step E9 making it possible to check whether the total arc energy is greater than or equal to a threshold of critical energy Z (for example expressed in Joules). In other words, during step E8, the following test is carried out: $$E_{\mathit{arctot}}\ge Z?$$

For example, the threshold Z is equal to 2 Joules. However, the value of this threshold could be adapted according to the installation and its environment.

If the test E9 is positive, the total arc energy having reached or exceeded the threshold Z, the energy evaluation device 8 automatically sends the intervention device 9 a command to secure the installation 100 Then, during a step E9, the intervention device 9 secures the photovoltaic installation 100. This security can be based on switches controlled remotely. It can consist of an order of interruption of the operation of the photovoltaic installation, which makes it possible to stop the parasitic electric arc and to eliminate any risk of degradation and / or beginning of fire.

If the test E9 is negative, the total arc energy being lower than the threshold Z, the steps E6 to E9 are repeated for the next acquisition window (j = j + 1).

• « niveau 1 » correspondant à une énergie totale d'arc E_arctot (t) strictement inférieure à 1 Joules ;
• « niveau 2 » correspondant à une énergie totale d'arc E_arctot (t) supérieure ou égale à 1 Joules et strictement inférieure à 2 Joules ;
• « niveau 3 » correspondant à une énergie totale d'arc E_arctot (t) supérieure strictement à 2 Joules.

As a variant, different levels of criticality of the electric arc could be defined, for example:

• "Level 1" corresponding to a total arc energy E _arctot ( t ) strictly less than 1 Joules;
• "Level 2" corresponding to a total arc energy E _arctot ( t ) greater than or equal to 1 Joules and strictly less than 2 Joules;
• "Level 3" corresponding to a total arc energy E _arctot ( t ) greater than strictly 2 Joules.

Level 1 corresponds to an electric arc without risk of safety. The evaluation device 8 may possibly signal the presence of an electric arc without risk of safety to an operator. He may decide not to activate an alert for this level.

Level 2 corresponds to an electric arc without risk of immediate safety but which could possibly become dangerous. In this case, the evaluation device 8 signals to the operator the presence of an electric arc without risk of immediate safety but requiring a rapid intervention to identify the defect at the origin of the arc and correct it.

Level 3 corresponds to a dangerous electric arc. The evaluation device 8 controls an immediate security of the photovoltaic system 100 to the intervention device 9, as previously described.

In the embodiment just described, the detected electric arc (as shown in FIG. figure 3 ) is a continuous arc of long duration. In another embodiment, the detected electric arc is discontinuous. It comprises a succession of micro-arcs separated by periods without arc. On the figure 4 , there is shown an example of discontinuous electric arc during an acquisition window, in this case the window containing the first micro-arcs. In this case, the energy evaluation device 8 identifies the micro-arcs and, for each micro-arc, determines the average value of the current during this micro-arc and then evaluates the corresponding voltage value as previously explained. Then he evaluates the energy of each micro-arc. The device 8 stores in memory the evaluated energies relative to the micro-arcs identified then sum these energies in order to obtain the total energy generated by the electric arc. The test E9 is then implemented so as to order a safe setting of the photovoltaic system 100.

Claims (15)

1. A method for evaluating the electrical energy produced by an electric arc in a photovoltaic installation (100), comprising the following steps:

   D) Measuring (E0) an electric current signal produced by the installation (100) at a sampling frequency greater than or equal to 50 kHz and, from the measured current signal:

   ∘ Determining (E3) an initial value (lo) of the current before an electric arc appears;

   ∘ Determining (E5) current values (I_arcj) during the electric arc;

   E) Evaluating (E6) values of an arc voltage from the current values determined during the arc and from the initial value of the current;

   F) Integrating (E7), over time, the product of the evaluated arc voltage values and the determined current values, in order to determine the energy of the arc.
2. The method as claimed in claim 1, characterized in that, to evaluate each arc voltage value, the difference between a determined current value during the arc and the initial current value is calculated, and said difference is multiplied by the ratio between a magnitude of a voltage jump (ΔV_arc0) linked to the appearance of the electric arc and a magnitude of a current jump (ΔI_arc0) linked to the appearance of the electric arc.
3. The method as claimed in either of the preceding claims, characterized in that it comprises a step (E1) of breaking down the current signal into a plurality of acquisition windows (F_x, F_i, F_arcj), and, for each acquisition window, a step (E5) of determining an average value of the current, said average value being recorded in memory.
4. The method as claimed in the preceding claim, characterized in that, in the integration step (E7), an arc energy for each acquisition window is calculated (E7a) by taking the product of the average value of the current measured over said window, of the evaluated voltage value and of a duration of the acquisition window, and then summing (E7b) the calculated arc energies in relation to a succession of acquisition windows.
5. The method as claimed in one of the preceding claims, characterized in that, in the event of a discontinuous electric arc including a plurality of micro-arcs, steps B) and C) are implemented in order to determine the energy of each electric micro-arc, and then the respective energies of the electric micro-arcs are summed in order to determine the energy of the discontinuous electric arc.
6. The method as claimed in one of the preceding claims, characterized in that the initial value of the current (lo) is equal to the average value of the current in relation to at least one acquisition window (F_N) preceding the one that contains the current jump.
7. The method as claimed in one of the preceding claims, characterized in that the magnitude of the voltage jump is predefined and between 12 V and 35 V, in particular equal to 20 V.
8. The method as claimed in one of the preceding claims, characterized in that the magnitude of the current jump is determined from the measured current signal.
9. The method as claimed in one of the preceding claims, characterized in that it comprises a step (E8) of comparing the determined energy of the electric arc with an energy threshold, and a protection step (E9) if said threshold is exceeded.
10. A device for evaluating the energy released by an electric arc in a photovoltaic installation (100), characterized in that it comprises:

    • a module (80) for obtaining an electric current signal produced by the installation;

    • a module (81) for processing the current signal, designed to determine an initial value of the current before an electric arc appears and current values during the electric arc;

    • a module (82) for evaluating arc voltage values from the determined current values and from the initial value of the current;

    • a module (83) for integrating, over time, the product of the evaluated arc voltage values and the determined current values, in order to determine the energy of the arc.
11. The device as claimed in the preceding claim, characterized in that the module (82) for evaluating arc voltage values is designed to calculate the difference between a determined current value during the arc and the initial current value and multiply said difference by the ratio between a magnitude of a voltage jump (ΔV_arc0) linked to the appearance of the electric arc and a magnitude of a current jump (ΔI_arc0) linked to the appearance of the electric arc.
12. The device as claimed in either of claims 10 and 11, characterized in that the module (81) for processing the current signal is designed to break down the current signal into a plurality of acquisition windows, and, for each acquisition window, determine an average value of the current measured over said window, said average value of the current being recorded in memory.
13. The device as claimed in the preceding claim, characterized in that the integration module (83) is designed to calculate, for each acquisition window, an arc energy by taking the product of the average value of the current measured over said window, of the evaluated voltage value and of a duration of the acquisition window, and then to sum (E7b) the calculated arc energies in relation to a succession of acquisition windows.
14. A safety system for a photovoltaic installation, characterized in that it comprises a device (7) for detecting an electric arc, a device (8) for evaluating the energy released by the detected electric arc, as claimed in one of claims 10 to 13, and an intervention device (9) intended to protect the photovoltaic installation in the event of an electric arc.
15. A photovoltaic installation, characterized in that it comprises a safety system as claimed in the preceding claim.

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